The Bio::SearchDist object is a wrapper around Sean Eddy's excellent histogram object. The histogram object can bascially take in a number of scores which are sensibly distributed somewhere around 0 that come from a supposed Extreme Value Distribution. Having add all the scores from a database search via the add_score method you can then fit a extreme value distribution using fit_evd(). Once fitted you can then get out the evalue for each score (or a new score) using evalue($score).

The fitting procedure is better described in Sean Eddy's own code (available from http://hmmer.janelia.org/, or in the histogram.h header file in Compile/SW). Bascially it fits a EVD via a maximum likelhood method with pruning of the top end of the distribution so that real positives are discarded in the fitting procedure. This comes from an orginally idea of Richard Mott's and the likelhood fitting is from a book by Lawless [should ref here].

The object relies on the fact that the scores are sensibly distributed around about 0 and that integer bins are sensible for the histogram. Scores based on bits are often ideal for this (bits based scoring mechanisms is what this histogram object was originally designed for).

User feedback is an integral part of the evolution of this and other Bioperl modules. Send your comments and suggestions preferably to one of the Bioperl mailing lists. Your participation is much appreciated.

rather than to the module maintainer directly. Many experienced and reponsive experts will be able look at the problem and quickly address it. Please include a thorough description of the problem with code and data examples if at all possible.